The present invention relates to an elevator installation with a car and a device for determining a car position and to a method of operating such an elevator installation.
Determining the car position of an elevator installation to derive from this information control signals which are subsequently used by the elevator control is known. Thus, German utility model DE9210996U1 describes a device for determining the car position by means of a magnetic strip and a magnetic head for reading the magnetic strip. The magnetic strip has a magnetic coding and extends along the entire length of travel of the car. The magnetic head which is mounted on the car reads the coding contactlessly. From the coding which is read, a car position is determined.
A further development of this device is disclosed in patent specification WO 03011733A1. According to the description contained in that patent specification, the coding of the magnetic strip consists of a multiplicity of code marks arranged in a line. The code marks are magnetized either as a north pole or as a south pole. Several code marks following in sequence form a code word. The code words themselves are arranged in a sequence as code mark patterns with pseudo-random coding. Thus, each code word represents an absolute car position.
For the purpose of scanning the magnetic fields of the code marks, the device of the patent specification WO 03011733A1 has a sensor device with a plurality of sensors which enables simultaneous scanning of a plurality of the code marks. The sensors convert the different polarities of the magnetic fields into corresponding binary information. For south poles they generate a bit value of “0” and for north poles a bit value of “1”. This binary information is analyzed by an analyzer of the device and converted into an absolute position indication which can be understood by the elevator control and used by the elevator control as a control signal. When detecting the magnetic field of the code marks, the resolution of the absolute car position is equal to the length of one code mark, i.e. 4 mm.
The patent specification WO 03011733A1 also describes the use of small, 3 mm long sensors which are arranged in two rows on adjacent tracks so that along the length of one code mark two sensors take up positions which are offset relative to each other along the length of travel by half a pole distance (λ/2). This arrangement of the sensors has the effect that when the sensors of one row detect a position in the area between two code marks (poles) the sensors of the other row are each in the optimal reading area over a code mark. This ensures that at each occurrence of sensing, to determine the position, that row of sensors is always analyzed whose sensors are positioned in the optimal detection area over the code marks at the moment when sensing occurs.
Disadvantageous in the device of the patent specification WO 03011733A1 is firstly that the sensors must be guided centered with great accuracy of ±1 mm perpendicular to the direction of travel so that the sensors always move within the allowable lateral deviation from the line of the code marks which is given by the lateral boundaries of readability of the magnetic fields of the code marks. In this connection it should be remembered that the strength of the magnetic fields—hereinafter also referred to as the signal strength—diminishes in the direction of the side edges of the code marks.
Also disadvantageous in this known device is that the strength of the magnetic field diminishes rapidly in the perpendicular direction above the code marks and the sensors must therefore be positioned at a small distance of 3 mm above the code marks. For adequate certainty and sufficient reliability of the elevator installation, the sensor device must be elaborately guided over the code mark pattern. This is expensive. Particularly in the case of high car speeds of 10 meters per second the associated outlay is very large.